Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932301AbdHVIay (ORCPT ); Tue, 22 Aug 2017 04:30:54 -0400 Received: from LGEAMRELO13.lge.com ([156.147.23.53]:39537 "EHLO lgeamrelo13.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932238AbdHVIad (ORCPT ); Tue, 22 Aug 2017 04:30:33 -0400 X-Original-SENDERIP: 156.147.1.125 X-Original-MAILFROM: byungchul.park@lge.com X-Original-SENDERIP: 10.177.222.33 X-Original-MAILFROM: byungchul.park@lge.com From: Byungchul Park To: peterz@infradead.org, mingo@kernel.org Cc: joel.opensrc@gmail.com, linux-kernel@vger.kernel.org, juri.lelli@gmail.com, rostedt@goodmis.org, kernel-team@lge.com Subject: [PATCH v9 2/2] sched/rt: Add support for SD_PREFER_SIBLING on find_lowest_rq() Date: Tue, 22 Aug 2017 17:30:15 +0900 Message-Id: <1503390615-22342-3-git-send-email-byungchul.park@lge.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1503390615-22342-1-git-send-email-byungchul.park@lge.com> References: <1503390615-22342-1-git-send-email-byungchul.park@lge.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3964 Lines: 131 Hello Steven, I added several comments so I'm not sure if I could add your reviewed-by. ----->8----- >From f0710d99759ed28c1409a527166780899f00d236 Mon Sep 17 00:00:00 2001 From: Byungchul Park Date: Tue, 22 Aug 2017 17:19:21 +0900 Subject: [PATCH v9 2/2] sched/rt: Add support for SD_PREFER_SIBLING on find_lowest_rq() It would be better to try to check other siblings first if SD_PREFER_SIBLING is flaged when pushing tasks - migration. Signed-off-by: Byungchul Park Suggested-by: Peter Zijlstra --- kernel/sched/rt.c | 78 ++++++++++++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 75 insertions(+), 3 deletions(-) diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index 979b734..196ffc7 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -1618,12 +1618,35 @@ static struct task_struct *pick_highest_pushable_task(struct rq *rq, int cpu) static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask); +/* + * Find the first cpu in: mask & sd & ~prefer + */ +static int find_cpu(const struct cpumask *mask, + const struct sched_domain *sd, + const struct sched_domain *prefer) +{ + const struct cpumask *sds = sched_domain_span(sd); + const struct cpumask *ps = prefer ? sched_domain_span(prefer) : NULL; + int cpu; + + for_each_cpu(cpu, mask) { + if (!cpumask_test_cpu(cpu, sds)) + continue; + if (ps && cpumask_test_cpu(cpu, ps)) + continue; + break; + } + + return cpu; +} + static int find_lowest_rq(struct task_struct *task) { - struct sched_domain *sd; + struct sched_domain *sd, *prefer = NULL; struct cpumask *lowest_mask = this_cpu_cpumask_var_ptr(local_cpu_mask); int this_cpu = smp_processor_id(); int cpu = task_cpu(task); + int fallback_cpu = -1; /* Make sure the mask is initialized first */ if (unlikely(!lowest_mask)) @@ -1668,9 +1691,35 @@ static int find_lowest_rq(struct task_struct *task) return this_cpu; } - best_cpu = cpumask_first_and(lowest_mask, - sched_domain_span(sd)); + /* + * If a cpu being in lowest_mask & current sd & + * ~prefer sd is valid, that becomes our choice. + * Of course, the lowest possible cpu is already + * under consideration through lowest_mask. + */ + best_cpu = find_cpu(lowest_mask, sd, prefer); + if (best_cpu < nr_cpu_ids) { + /* + * If current domain is SD_PREFER_SIBLING + * flaged, we have to try to check other + * siblings first. + */ + if (sd->flags & SD_PREFER_SIBLING) { + prefer = sd; + + /* + * fallback_cpu should be one + * in the closest domain among + * SD_PREFER_SIBLING domains, + * in case that more than one + * SD_PREFER_SIBLING domains + * exist in the hierachy. + */ + if (fallback_cpu == -1) + fallback_cpu = best_cpu; + continue; + } rcu_read_unlock(); return best_cpu; } @@ -1679,6 +1728,29 @@ static int find_lowest_rq(struct task_struct *task) rcu_read_unlock(); /* + * If fallback_cpu is valid, all our guesses failed *except* for + * SD_PREFER_SIBLING domain. Now, we can return the fallback cpu. + * + * XXX: Consider the following example, 4 cores SMT2 system: + * + * LLC [0 - 7] + * SMT [0 1][2 3][4 5][6 7] + * o x o x x x x x + * + * where 'o': occupied and 'x': empty. + * + * A wakeup on cpu0 will exclude cpu1 and choose cpu3, since + * cpu1 is in a SD_PREFER_SIBLING sd and cpu3 is not. However, + * in this case, we have to choose cpu4 for better work, instead + * of cpu3 that is fully loaded. + * + * We have to do the best if possible, but choose the second + * best here since that is too expensive to adopt. + */ + if (fallback_cpu != -1) + return fallback_cpu; + + /* * And finally, if there were no matches within the domains * just give the caller *something* to work with from the compatible * locations. -- 1.9.1